• Structural Engineering and Mechanics
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• v.26 no.6
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• pp.651-672
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• 2007

This study presents an improved method that uses the elastic and inelastic system buckling analyses for determining the K-factors of steel column members. The inelastic system buckling analysis is based on the tangent modulus theory for a single column and the application is extended to the frame structural system. The tangent modulus of an inelastic column is first derived as a function of nominal compressive stress from the column strength curve given in the design codes. The tangential stiffness matrix of a beam-column element is then formulated by using the so-called stability function or Hermitian interpolation functions. Two inelastic system buckling analysis procedures are newly proposed by utilizing nonlinear eigenvalue analysis algorithms. Finally, a practical method for determining the K-factors of individual members in a steel frame structure is proposed based on the inelastic and/or elastic system buckling analyses. The K-factors according to the proposed procedure are calculated for numerical examples and compared with other results in available references.

• Structural Engineering and Mechanics
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• v.65 no.4
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• pp.401-408
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• 2018

Concentric braced frames are commonly used in steel structures to withstand lateral forces. One of the drawbacks of these systems is the possibility that the braces are buckled under compressive loads, which leads to sudden reduction of the bearing capacity of the structure. To overcome this deficiency, the idea of the Buckling Restrained Brace (BRB) has been proposed in recent years. The length of a BRB steel core can have a significant effect on its overall behavior, since it directly influences the energy dissipation capability of the member. In this study, numerical methods have been utilized for investigation of the optimum length of BRB steel cores. For this purpose, BRBs with different lengths placed into several two-dimensional framing systems with various heights were considered. Then, the Response History Analysis (RHA) was performed, and finally, the optimum steel core length of BRBs and its effect on the responses of the overall system were investigated. The results show that the shortest length where failure does not occur is the best length that can be proposed as the optimum steel core length of BRBs. This length can be obtained through a formula which has been derived and verified in this study by both analytical and numerical methods.

• Journal of Korean Society of Steel Construction
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• v.19 no.1
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• pp.129-137
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• 2007

In this study, the elastic out-of-plane buckling load and the effective length factor of X-bracing systems were studied. Points of the intersection of diagonals were modeled as a rigid connection or a pinned connection depending on the connection method of diagonals. The boundary condition of the intersection influences the buckling load of X-bracing systems. For each boundary condition of the intersection, effective out-of-plane length factors of X-bracing systems were derived as a function of the length ratio of tension and compression diagonals $L_P$/$L_T$, the applied force ratio of tension and compression diagonals T/P, and the Euler buckling load ratio of tension and compression diagonals $P_{ET}$/$P_{EP}$. The proposed effective out-of-plane length factors of X-bracing systems were compared with the results of previous researchers and those of the finite element analysis and their properties were verified. Finally, the effects of the boundary condition of the intersection on the out-of-plane buckling load of X-bracing systems were investigated.

• Structural Engineering and Mechanics
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• v.19 no.1
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• pp.55-71
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• 2005

In several design codes and specifications, simplified formulae and diagrams are given for determining the buckling lengths of frame columns. It is shown that these formulae may yield rather erroneous results in certain cases. This is due to the fact that, the code formulae utilise only local stiffness distributions. In this paper, a simplified procedure for determining approximate values for the buckling loads of multi-storey frames is developed. The procedure utilises lateral load analysis of frames and yields errors in the order of 10%, which may be considered suitable for design purposes. The proposed procedure is applied to several numerical examples and it is shown that all the errors are in the acceptable range and on the safe side.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.841-844
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• 1997

Sandwich structure is widely used in various fields of industry due to its excellent strength and stiffness compared with weight. We studied the buckling and bending behavior with respect to the variation of design parameters such as length, height, and thickness of honeycomb sandwich core. We found that as the density and the thickness of core become higher, the value of critical bucking load increased significantly. We found that the effect of bending stress due to critical buckling load resulted in high bending stress and the value of bending stress decreased in half according to the increase of length of core. The effect by bending stress is dominant above the portion of the intersection line between bending stress and the effect of buckling is dominant below the potion of it. We could get proper thickness ratio and density of core according to applied load conditions.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.993-1000
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• 2006

Practical stability design method of main members of cable-stayed bridges is proposed and discussed through a design example. For this purpose, initial tensions of stay cables and axial forces of main members are firstly determined using initial shaping analysis of bridges under dead loads. And then the effective buckling length using system elastic/inelastic buckling analysis and bending moments considering $P-{\delta}-{\Delta}$ effect by second-order elastic analysis are calculated for main girder and pylon members subjected to both axial forces and moments, respectively. Particularly, load combinations of dead and live loads, in which maximum load effects due to live loads are obtained, are taken into account and effects of live loads on effective buckling lengths are investigated.

• Journal of the Korean Society for Railway
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• v.13 no.2
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• pp.147-151
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• 2010

Since the kinetic energy is dissipated through plastic deformation energy generated in expanding process of the tube by a die. In order to successfully absorb the kinetic energy there should be no buckling in the expansion tube during expanding process. The buckling instability of the expansion tubes is affected by the initial boundary conditions, tube thickness and length. In this study, the effects of the tube thickness except length and initial boundary condition on the buckling instability are studied using a finite element method. In addition, Analysis procedure for nonlinear post-buckling analysis of expansion tube is established. There are three kinds of finite element analysis procedures for buckling analysis of expansion tube, quasi-static analysis, linear buckling analysis and nonlinear post-buckling analysis. The effect of the geometry imperfections defined as linear superimposition of buckling modes is considered in the nonlinear post-buckling analysis. The results of finite element analysis indicate that the buckling load increase with increase of thickness of tube and geometry imperfection. Finial buckling shapes are changed with respect to the geometry imperfection.

• Structural Engineering and Mechanics
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• v.9 no.5
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• pp.417-432
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• 2000

A comprehensive analytic study has been conducted to investigate the instability problems of metal-plate-connected (MPC) joints in light frame trusses. The primary objective in this study is to determine the governing factors that constitute the buckling of the metal connectors and their effects on the structural response of joints. Another objective is to recommend design curves for the daily structural design of these joints. The numeric data presented in this paper has emerged from a broad base that was founded on over 350 advanced computer simulations, and was supported by available experimental results obtained by others. This basic-to-applied research includes practical engineering parameters such as size of gaps, shear lengths, gauge (plate thickness) of connectors, size of un-braced areas, failure modes, and progressive disintegration of joints. Square-end members have been emphasized though the results cover the custom-made fitted joints. The results indicate that chord shears cause and dominate the buckling of MPC joints, and the shear length has a more pronounced effect than the size of gaps. Further, large gauges and small un-braced areas improve the buckling response. Several practical recommendations have been suggested throughout the paper such as keeping the ratio of gap/shear length below 3/4 for improving the buckling strength. The study reveals that multi-area joints should not be simplified as single web-to-chord MPC joints such as keeping the ratio of gap/shear length below 3/4 for improving the buckling strength, even where one web is in tension and the other in compression. Finally, the results obtained from this study favorably agree with experimental data by others, and the classic buckling theories for other structural components.

• Journal of Korean Society of Steel Construction
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• v.10 no.2 s.35
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• pp.253-261
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• 1998

The buckling length of exterior beam-columns of the first floor in moment resisting steel frames with weak beams is uncertain when plastic hinges occur at the ends of weak beams due to seismic loads. The objective of this study is to investigate the buckling strength of concrete-filled tubular beam-columns and to suggest the reduced buckling length of them to apply to the beam-column design code. The exterior beam-columns are modelized with horizontal displacement restraint springs. Their strength and reduced buckling length are evaluated by numerical analysis.

• Structural Engineering and Mechanics
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• v.73 no.3
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• pp.225-238
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• 2020

This work treats the axisymmetric buckling of functionally graded (FG) porous annular/circular nanoplates based on modified couple stress theory (MCST). The nanoplate is located at the elastic medium which is simulated by Kerr foundation with two spring and one shear layer. The material properties of the porous FG nanostructure are assumed to vary through the nanoplate thickness based on power-law rule. Based on two variables refined plate theory, the governing equations are derived by utilizing Hamilton's principle. Applying generalized differential quadrature method (GDQM), the buckling load of the annular/circular nanoplates is obtained for different boundary conditions. The influences of different involved parameters such as boundary conditions, Kerr medium, material length scale parameter, geometrical parameters of the nanoplate, FG power index and porosity are demonstrated on the nonlinear buckling load of the annular/circular nanoplates. The results indicate that with increasing the porosity of the nanoplate, the nonlinear buckling load is decreased. In addition, with increasing the material length scale parameter to thickness ratio, the effect of spring constant of Kerr foundation on the buckling load becomes more prominent. The present results are compared with those available in the literature to validate the accuracy and reliability. A good agreement is observed between the two sets of the results.